Click the green flag. Press space to see the next stereogram. (There are 11.) Full screen is highly recommended. (Unless your screen is the size of a TV.) To see the stereogram, you have to diverge your eyes. As you can see, there's a repeating pattern that changes a little bit. You need to have your eyes pointed so that the left eye looks straight at one pattern, while the right eye looks straight at the pattern just to the right of it. When you are looking at something far away in real life, your eyes naturally diverge like that.
I made these sterograms with a stereogram editing program I coded with Visual Basic. Visual Basic edits pictures in just a second, compared to Scratch taking several minutes. The GetColor() command helps a lot.